Carnitine is required for eukaryotic cells to derive energy from long chain fatty acids. Carnitine nutriture has gone relatively unnoticed in the past. The newborn has very low tissue carnitine levels and normally receives carnitine from the mother's milk. However, non-milk-based infant formulas contain very little carnitine. The proposed experiments will determine if newborn rats fed a carnitine deficient formula can synthesize enough carnitine to supply the needs of the body. The rate of carnitine biosynthesis in the newborn will be measured and compared to that of the adult. During normal development, tissues of male and female rats accumulate carnitine differently such that adult male rats have more carnitine in plasma, cardiac muscle, and skeletal muscle than do female rats, but female rats have more liver carnitine than do male rats. Removal of the pituitary, testes, or ovaries of the weanling animal alters the levels of tissue carnitine when the animals reach adulthood. The effect of hormone replacement therapy on the rate of carnitine biosynthesis in the liver and on tissue carnitine levels in these animals will be tested. During the past five years several young people with muscle weakness have been shown to have low levels of carnitine in muscle. An altered mechanism of controlling tissue carnitine levels during development may be the lesion responsible for the low levels of carnitine seen in these patients. Experiments are designed to elucidate the factors which regulate tissue carnitine levels during normal development.